Tagatose is a natural sweetener present only in small amounts in foods such as milk, cheese, cacao, and the like and in naturally sweet fruits such as apples, mandarins, and the like, and has physical properties similar to sucrose. Tagatose has a low-calorie value of 1.5 kcal/g corresponding to one-third that of sucrose and glycemic index (GI) of 3 corresponding to 5% that of sucrose. Tagatose has a sweet taste similar to sucrose and has various health and functional characteristics, and thus has been used in various products as an alternative sweetener capable of satisfying both taste and health.
Tagatose can be produced from galactose, as a raw material, by a chemical isomerization (catalytic reaction) method and a biological (enzymatic isomerization reaction) method (see Korean Patent Publication No. 2009-0082774 A). However, the price of lactose, which is a raw material for tagatose, is unstable depending on produced amounts, supply of and demand for raw milk and lactose on the global market, and the like, and such a price fluctuation in raw milk makes stable supply of raw materials for tagatose production difficult. Therefore, there is a need for a new method for producing tagatose using general saccharides (sucrose, glucose, fructose, and the like).